Instabilities in semiconductor heterostructure growth can be exploited for the self-organized formation of nanostructures, allowing for carrier confinement in all three spatial dimensions. Beside the description of various growth modes, the experimental characterization of structural properties, such as size and shape, chemical composition, and strain distribution is presented. The authors discuss the calculation of strain fields, which play an important role in the formation of such nanostructures and also influence their structural and optoelectronic properties. Several specific materials systems are surveyed together with important applications.

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Structural properties of self-organized semiconductor nanostructures

Bismuth selenide is a prototypical 3D topological insulator; its electronic spectrum features a Dirac cone populated by surface states. Now, it is experimentally and numerically shown that a bandgap forms beyond a certain critical compressive strain, destroying the surface states.

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Tuning Dirac states by strain in the topological insulator Bi 2 Se 3

We present a cross-sectional scanning-tunneling microscopy investigation of the shape, size, and composition of InAs quantum dots in a GaAs matrix, grown by molecular beam epitaxy at low growth rate. From the dimensional analysis we conclude that the investigated quantum dots have an average height of 5 nm, a square base of 18 nm oriented along [010] and [100] and the shape of a truncated pyramid. From outward relaxation and lattice constant profiles we conclude that the dots consist of an InGaAs alloy and that the indium concentration increases linearly in the growth direction. Our results justify the predictions obtained from previous photocurrent measurements on similar structures and the used theoretical model.

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Determination of the shape and indium distribution of low-growth-rate InAs quantum dots by cross-sectional scanning tunneling microscopy

A few mololayers of InAs is heteroepitaxially grown on GaAs substrate by molecular‐beam epitaxy. Structure and optical properties are investigated. Reflection high‐energy electron‐diffraction observation reveals that an InAs layer forms a three‐dimensional structure with specific facets after two‐dimensional growth. The transmission electron microscope observation shows that these structures have structural anisotropy in the growth plane. Photoluminescense spectroscopy shows that the luminescence from the InAs structures exhibits the polarization property caused by the quantum dot effect of the structural anisotropy.

Initial growth stage and optical properties of a three‐dimensional InAs structure on GaAs

GaAs(001) has been one of the most intensively studied surfaces for the past 30 years due both to its importance as a substrate for epitaxial growth and to the challenge its phase diagram of complex structures presents to computational methods. Yet despite substantial experimental and theoretical effort, a number of fundamental questions remain concerning growth kinetics and mechanisms on this surface, even for homoepitaxy, but more especially in the formation of heterostructures. These issues have acquired a renewed timeliness because the quantum dots that are formed during the Stranski–Krastanov (SK) growth of InAs on GaAs(001) can be used for optoelectronic applications and have potential in quantum dot-based architectures for quantum computing. In this review we survey the current state of understanding of growth kinetics on GaAs surfaces, beginning with the simplest case, homoepitaxy on GaAs(001). We compare interpretations of recent reflection high energy electron diffraction measurements taken during the initial stages of growth with predictions of ab initio density functional calculations. We also consider the extent to which snapshot scanning tunnelling microscopy images from rapidly quenched samples truly reflect the growing surface structure as revealed by in situ real-time methods. We then examine the present experimental and theoretical status of the SK growth of InAs quantum dots on singular orientations of low-index GaAs surfaces, focussing on such issues as the importance of substrate orientation and surface reconstruction of the substrate, wetting layer formation, the nucleation kinetics of quantum dots, their size distributions and the role of strain. The systematics and anomalies of the phenomenology will be highlighted, as well as the current understanding of quantum dot formation.

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Self-organized growth on GaAs surfaces

We present a quantitative technique for the direct compositional analysis of quantum dots (QDs), in which scanning transmission electron microscopy is applied to a capped InAs/GaAs QD layer in a structure also containing InxGa1−xAs/GaAs quantum well (QW) layers to provide an internal calibration of the In content. By obtaining energy dispersive x-ray analysis line scans through both QWs and QDs, the composition of the QDs can be determined by reference to the known composition of the QWs. In this article the method is described and demonstrated using two InAs/GaAs structures in which the QDs are nominally identical, but with different In composition in the calibration QW layers. We find that the QDs in both structures have an In composition of 65%–67% and the associated wetting layers contain approximately 12% In.

D.W. Pashley

Papers

Quantitative compositional analysis of InAs/GaAs quantum dots by scanning transmission electron microscopy

A model for the appearance of chevrons on RHEED patterns from InAs quantum dots

The morphology and asymmetric strain relief behaviour of InAs films on GaAs (110) grown by molecular beam epitaxy

Dislocation displacement field at the surface of inas thin films grown on gaas(110)

A transmission electron microscopy (TEM) study of a wedge-shaped InAs epitaxial layer on GaAs (001) grown by molecular beam epitaxy (MBE)